From Amy Maxmen at Nature News:
tenOever speculates that RNAse III proteins originally helped bacteria to maintain their own RNA, and that bacteria later deployed the proteins against the genetic material of viruses. He points out the occurrence of RNAse III proteins in immune responses throughout the tree of life. For instance, some CRISPR systems, a virus-fighting response in archaea and bacteria, include RNAse III proteins. Plants and invertebrates deploy the proteins in RNAi. And although vertebrates rely on interferons for viral control, this study now shows that Drosha still chases after viruses, in the same way a pet Golden Retriever — a dog bred to retrieve waterfowl — fetches a stick as if it were a fallen duck.
Donald Court, a geneticist at the National Cancer Institute in Frederick, Maryland, calls the finding cool, but he doesn’t buy the evolutionary scenario. “RNAse III is involved in many things, in almost all domains of life,” he explains. He sees no reason to think that one antiviral system evolved into the next. For instance, he says, the fact that one CRISPR system includes RNAse III whereas others don’t suggests that the proteins were probably deployed acquired independently and not inherited. More.
Researchers sound more interesting when they are allowed their doubts.
See also: Did giant viruses evolve from smaller viruses? Or devolve from cells?
Here is a site on giant viruses.
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